Thursday, February 27, 2014

The Hydra v2.2 boards came in today, but I've had trouble in the past with the high-current path of both the OpenEVSEs and Hydras that I've built so far. I've come to the basic conclusion that engineering things that handle 30A of electrical power is a very unforgiving pursuit.

But with help from the OpenEVSE community, I may have finally cracked it.

I had been using crimp on .25" QD terminals I got at Home Depot, but it appears that those just aren't good enough for that kind of high current application. Instead, I've gotten in a supply of Molex Avikrimp terminals (DigiKey WM18256-ND), and with my ratcheting crimping tool, those appear to crimp on much more firmly. It takes a lot more effort to close the tool, and the resulting connector just feels a lot more solid.

The downside is that they don't fit very well in the Cooper Bussmann power distribution block I've been using.

There is the Cooper Bussmann 16220-2 instead of the 11725-2. That has four screw terminals on the load side instead of 4 QD terminals. But it costs $55 instead of $17.

Saturday, February 8, 2014

I'm pretty happy with the stuff I've been able to design so far. But I feel stuck, a little. What's next?

I had thought of attempting to make a contemporary design of a vintage computer. Like a completely SMD CP/M machine. A Z-80 with 64K of RAM, say, 16K of flash and an SD card slot. But why? You can get a Raspberry Pi for $40 and run a Z-80 emulator on it.

Saturday, February 1, 2014

The second and final RS-232 board came in. The big change was an SSOP line driver in place of the SOIC one. I also decided to use the super-bright LEDs on it, just for fun. There's no missing them when they blink!

The first prototype on the bottom, the new one on top.

I still don't know what to do next. I can sell them for about $15 with low parts purchase quantities, but that doesn't include a case or a µUSB cable. I could lower that price if I were making thousands of them, but what market there is for USB-to-RS232 cables is saturated.

The other thing I built was the final version of the i2c RGB LCD backpack display. As a reminder, this is like the OpenEVSE display, but instead of just a SELECT button, I've included a 5 way tactile switch and a piezo element supported by the LiquidTWI2 "buzz" method. You can also change the i2c address of the GPIO chip with 2 way solder jumpers and you can change the common backlight pin from common cathode to common anode with another. In fact, this prototype is hooked up to a SparkFun RGB LCD display that has a common anode backlight. You just need to change an initialization constant in your LiquidTWI2 setup and it works exactly the same way.